#include<bits/stdc++.h>
using namespace std;
int main()
{
    //1 1 2 3 5 8 13 21
    long long a[50];
    a[1]=1;a[2]=1;
    for(int i=3;i<50;i++) a[i]=a[i-1]+a[i-2];
    int n;
    cin>>n;
    cout<<a[n]<<".00"<<endl;
    return 0;
}
//12344321